Direct Link Between Stress and Aggression

Oct. 13, 2004

— Scientists have found biological evidence that stress and aggression feed off of each other, contributing to a "cycle of violence" that can be tragic. When we are under stress, we are more likely to fly off the handle, and when we fly off the handle, that increases our level of stress.

It's a mutual back-scratching phenomenon, and new research shows that there is a biochemical basis for this potentially deadly spiral of stress and aggression.

Researchers in The Netherlands and Hungary found the biological connection in 53 rats, so it's not yet been demonstrated in humans, but that connection has held up in similar research in the past. They experimented with rats because it's possible to implant electrodes in the brain to turn on and off the stress sensors, and of course that sort of thing would be frowned upon if the subjects were humans.

Opening the Flood Gates

The researchers found that when they turned on the electrodes to convince the rats that they were in a stressful situation, the level of corticosterone soared upward in their bloodstreams. That's the major hormone produced by bodies -- both rats and humans -- to help us get through stressful situations.

What happened next was very revealing. The rats became very aggressive, even attacking other rats that had been drugged to the point that they were almost lifeless. That, in turn, stimulated the attacking rats to produce more of the hormone, thus plunging them into a hopeless cycle of stress and violence.

The researchers found they could turn the cycle on and off just by regulating the hormone, and the rats could care less that their opponents were under "profound sedation," according to a report on their study in the October issue of "Behavioral Neuroscience," which is published by the American Psychological Association.

It gets worse. The stressed rats didn't even need another rat to get riled up.

"The confrontation with an opponent apparently is not required," they report.

That "feedback mechanism," the researchers say, may explain why someone who has had a bad day at work may go home and take it out on his or her loved ones. That cycle of stress and aggression can, in extreme cases, be deadly.

That vicious cycle "would explain why aggressive behavior escalates so easily and is so difficult to stop once it has started," they add.

Lead author Menno R. Kruk of the Leiden/Amsterdam Center for Drug Research notes that stress hormones are supposed to prepare the body to either fight or flee in the presence of an enemy, but the research shows that the hormones "talk back'' to the brain to encourage fighting.

Lethal Emotion

Kruk and his colleagues believe their findings may help explain why a normal, peaceful chap who is not prone to violence can suddenly boil over, leading to road rage, spouse abuse or worse. That jerk ahead of you cut into your lane, sending your stress up, which in turn fed your aggressive side, sending your stress up even higher, and suddenly, bam.

The research is part of an odd reversal in our attitudes toward stress. For thousands of years, people recognized that stress could make us sick. But as more and more specific causes for various diseases became known, that common-sense perception of the impact of stress lost favor, at least among medical professionals.